Effects of organic matter on acidic electrolysed water for reduction of foodborne pathogens on lettuce and spinach

Aims: To evaluate the efficacy of acidic electrolysed water (EW) in the presence of organic matter (bovine serum) on the inoculated surfaces of lettuce and spinach. Materials and Results: Lettuce and spinach leaves were inoculated with a cocktail of three strains each of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes and treated with deionized water, acidic EW and acidic EW containing bovine serum (5, 10, 15 and 20 ml l^?1) for 15 s, 30 s, 1 min, 3 min and 5 min at room temperature (22 ± 2°C). In the absence of bovine serum, acidic EW treatment reduced levels of cells below the detection limit (0·7 log) in 5 min. In the presence of bovine serum, bactericidal activity of acidic EW decreased with increasing serum concentration. Conclusions: Organic matter reduces the effectiveness of acidic EW for reducing pathogens on the surfaces of lettuce and spinach. Significance and Impact of the Study: From a practical standpoint, organic matter reduces the efficacy of acidic EW. This study was conducted to confirm the effect of organic matter on the properties of acidic EW in the inactivation of foodborne pathogens on the surface of vegetables.     

Effect of continuous ohmic heating to inactivate Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in orange juice and tomato juice

Aims: The purpose of this study was to investigate the efficacy of continuous ohmic heating for reducing Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in orange juice and tomato juice. Methods and Results: Orange juice and tomato juice were treated with electric field strengths in the range of 25–40 V cm^?1 for different treatment times. The temperature of the samples increased with increasing treatment time and electric field strength. The rate of temperature change for tomato juice was higher than for orange juice at all voltage gradients applied. Higher electric field strength or longer treatment time resulted in a greater reduction of pathogens. Escherichia coli O157:H7 was reduced by more than 5 log after 60‐, 90‐ and 180‐s treatments in orange juice with 40, 35 and 30 V cm^?1 electric field strength, respectively. In tomato juice, treatment with 25 V cm^?1 for 30 s was sufficient to achieve a 5‐log reduction in E. coli O157:H7. Similar results were observed in Salm. Typhimurium and L. monocytogenes. The concentration of vitamin C in continuous ohmic heated juice was significantly higher than in conventionally heated juice (P < 0·05). Conclusions: Continuous ohmic heating can be effective in killing foodborne pathogens on orange juice and tomato juice with lower degradation of quality than conventional heating. Significance and Impact of the Study: These results suggest that continuous ohmic heating might be effectively used to pasteurize fruit and vegetable juices in a short operating time and that the effect of inactivation depends on applied electric field strengths, treatment time and electric conductivity.     

Effect of curli expression and hydrophobicity of Escherichia coli O157:H7 on attachment to fresh produce surfaces

Aim: To investigate the effect of curli expression on cell hydrophobicity, biofilm formation and attachment to cut and intact fresh produce surfaces. Methods and Results: Five Escherichia coli O157:H7 strains were evaluated for curli expression, hydrophobicity, biofilm formation and attachment to intact and cut fresh produce (cabbage, iceberg lettuce and Romaine lettuce) leaves. Biofilm formation was stronger when E. coli O157:H7 were grown in diluted tryptic soy broth (1 : 10). In general, strong curli‐expressing E. coli O157:H7 strains 4406 and 4407 were more hydrophobic and attached to cabbage and iceberg lettuce surfaces at significantly higher numbers than other weak curli‐expressing strains. Overall, E. coli O157:H7 populations attached to cabbage and lettuce (iceberg and Romaine) surfaces were similar (P > 0·05), indicating produce surfaces did not affect (P < 0·05) bacterial attachment. All E. coli O157:H7 strains attached rapidly on intact and cut produce surfaces. Escherichia coli O157:H7 attached preferentially to cut surfaces of all produce types; however, the difference between E. coli O157:H7 populations attached to intact and cut surfaces was not significant (P > 0·05) in most cases. Escherichia coli O157:H7 attachment and attachment strength (S_R) to intact and cut produce surfaces increased with time. Conclusions: Curli‐producing E. coli O157:H7 strains attach at higher numbers to produce surfaces. Increased attachment of E. coli O157:H7 on cut surfaces emphasizes the need for an effective produce wash to kill E. coli O157:H7 on produce. Significance and Impact of the Study: Understanding the attachment mechanisms of E. coli O157:H7 to produce surfaces will aid in developing new intervention strategies to prevent produce outbreaks.     

Antimicrobial potential of polyphenols extracted from almond skins

Aims: To evaluate the antimicrobial properties of flavonoid‐rich fractions derived from natural and blanched almond skins, the latter being a by‐product from the almond processing industry. Methods and Results: Almond skin extracts were tested against Gram‐negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, Serratia marcescens), Gram‐positive bacteria (Listeria monocytogenes, Enterococcus hirae, Staphylococcus aureus, Enterococcus durans) and the yeast Candida albicans. Almond skin fractions were found to have antimicrobial activity against L. monocytogenes and Staph. aureus in the range 250–500 μg ml^?1, natural skins showing antimicrobial potential against the Gram‐negative Salm. enterica. The interactions between three almond skin flavonoids were also evaluated with isobolograms. Conclusions: Pairwise combinations of protocatechuic acid, naringenin and epicatechin showed both synergistic and indifferent interactions against Salm. enterica and Staph. aureus. Antagonism was observed against L. monocytogenes with all combinations tested. Further studies need to be performed to understand the mechanisms responsible for these interactions. Significance and Impact of the Study: Almond skins are a potential source of natural antimicrobials.     

Variable agronomic practices, cultivar, strain source and initial contamination dose differentially affect survival of Escherichia coli on spinach

Aims: Greenhouse and field trials were conducted under different agronomic practices and inoculum doses of environmental Escherichia coli and attenuated E. coli O157:H7, to comparatively determine whether these factors influence their survival on leaves and within the rhizosphere. Methods and Results: Hydroponic conditions: E. coli spray‐inoculated at log 4 CFU ml^?1 was recovered from leaf surfaces at a mean population of 1·6 log CFU g^?1 at 15 days. E. coli O157:H7 sprayed at log 2 or 4 CFU ml^?1 levelled off on spinach leaf surfaces at a mean average population of 1·4 log CFU g^?1 after 14 days, regardless of initial dose. Quantitative recovery was inconsistent across leaf developmental age. Field conditions: Average populations of E. coli O157:H7 spray‐inoculated at log 1·45 or 3·4 CFU m^?2 levelled off at log 1·2 CFU g^?1 over a 14‐day period. Pathogen recovery from leaves was inconsistent when compared to regularly positive detection on basal shoot tissue. Pathogen recovery from soil was inconsistent among sampling locations. Moisture content varied up to 40% DW and was associated with 50% (P < 0·05) decrease in positive locations for E. coli O157:H7 but not for E. coli. Conclusions: Overall, similar populations of environmental E. coli and E. coli O157:H7 were recovered from plants despite differences in inoculum dose and agronomic conditions. Strain source had a significant impact on the quantitative level and duration of survival on leaves and in soil. Water availability appeared to be the determinant factor in survival of E. coli and E. coli O157:H7; however, E. coli showed greater environmental fitness. Significance and Impact of the Study: Persistence of surrogate, indicator E. coli and E. coli O157:H7, irrespective of variable growing conditions in spinach is predominantly limited by water availability, strain source and localization within the plant. These findings are anticipated to ultimately be adopted into routine and investigative pathogen testing protocols and mechanical harvest practices of spinach.     

Survival and colonization of Escherichia coli O157:H7 on spinach leaves as affected by inoculum level and carrier, temperature and relative humidity

Aims: To determine survival and colonization of Escherichia coli O157:H7 on spinach leaves as affected by inoculum level and carrier, temperature and relative humidity (r.h.). Methods and Results: Spinach leaves were inoculated with suspensions of E. coli O157:H7 in distilled water (DW) and 0·1% peptone water (PW) and incubated at 4, 12 and 25°C and 43, 85 and 100% r.h. The number of E. coli O157:H7 on leaves (5·6 or 1·9 log CFU per leaf) inoculated using DW as a carrier medium increased significantly at 25°C and 100% r.h. within 120 h but remained constant or decreased significantly under other test conditions. E. coli O157:H7 on leaves (5·4 log CFU per leaf) inoculated using PW as a carrier increased significantly within 72 and 24 h, respectively, at 12 or 25°C and 100% r.h.; counts using a low inoculum (2·2 log CFU per leaf) increased significantly within 24 h at 25°C. Conclusions: Escherichia coli O157:H7 can colonize on spinach leaves at 12 or 25°C in a 100% r.h. environment. Organic matter in the inoculum carrier may provide protection and nutrients which enhance survival and colonization. Significance and Impact of the Study: Colonization of E. coli O157:H7 on spinach leaves as affected by organic matter in the inoculum, temperature and r.h. was determined. These observations will be useful when developing strategies to prevent growth of E. coli O157:H7 on pre‐ and postharvest spinach.     

Development and evaluation of a new device to effectively detach micro-organisms from food samples

Aims: To develop a new instrument of great versatility for recovering micro‐organisms from all types of food samples and to compare the effects with existing sample preparation methods. Methods and Results: To detach micro‐organisms from large‐size unbroken food samples such as apples, carrots, potatoes and tomatoes without preprocessing, the Spindle apparatus was newly developed. The Spindle was used to effectively detach micro‐organisms from large‐size samples. In a comparative study involving 51 food samples, treatment with the Spindle and Stomacher showed that recovery of total aerobic micro‐organisms (naturally occurring mesophilic microflora) and foodborne pathogens (from samples inoculated with Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes) for both methods was highly correlated (R² = 0·98). Furthermore, diluents treated by the Spindle contained much less food debris than those treated by stomaching. Conclusions: These results indicate that Spindle is a novel, effective alternative method for detaching micro‐organisms from food samples including four kinds of large‐size samples without the need for preprocessing. Significance and Impact of Study: The Spindle might be used to widely detaching micro‐organisms from all types of food samples for microbiological assay.     

Recovery of E. coli O157 strains after exposure to acidification at pH 2

Aims: Rapid detection and selective isolation of E. coli O157:H7 strains have been difficult owing to the potential interference from background microflora present in high background food matrices. To help selectively isolate E. coli O157H7 strains, a useful plating technique that involved acidifying the cultures to pH 2 was evaluated with a large number of E. coli O157:H7 strains to ensure response to treatment was consistent across strains. Methods and Results: Escherichia coli O157, 46 strains including ATCC 35150, were acidified to pH 2 following enrichment and plated onto Tryptic Soy Agar + 0·6% Yeast Extract (TSA‐YE) and Sorbitol MacConkey Agar + cefixime and tellurite (CT‐SMAC). Samples were enumerated and modest decreases in plate counts were observed on TSA‐YE media, with a greater reduction observed on CT‐SMAC. Conclusions: The acid‐resistant character of E. coli O157:H7 is a consistent trait and may be used for improved isolation of the organism from mixed cultures. Significance and Impact of the Study: There was little difference observed between the commonly used laboratory strain E. coli O157:H7 35150 and 45 other strains of E. coli O157 when subjected to acidifying conditions prior to plating, demonstrating that an acid rinse procedure was equally effective across a wide variety of E. coli O157 strains and broadly applicable for isolating unknown strains from food samples.     

Quantification of Survival of Escherichia coli O157:H7 on Plants Affected by Contaminated Irrigation Water

Enterohemorrhagic E. coli O157: H7 (EHEC) is a major foodborne pathogen capable of causing diarrhea and vomiting, with further complications such as hemolytic‐uremic syndrome (HUS). The aim of this study was to use the real‐time PCR method to quantify the survival of Escherichia coli O157:H7/pGFP in phyllosphere (leaf surface), rhizosphere (volume of soil tightly held by plant roots), and non‐rhizosphere soils (sand and clay) irrigated with contaminated water and compare the results obtained between real‐time PCR method and conventional plate counts. The real‐time PCR probe was designed to hybridize with the (eae) gene of E. coli O157:H7. The probe was incorporated into real‐time PCR containing DNA extracted from the phyllosphere, rhizosphere, and non‐rhizosphere soils irrigated with water artificially contaminated with E. coli O157:H7. The detection limit for E. coli O157:H7 quantification by real‐time PCR was 2.3 × 10³ in the rhizosphere and phyllosphere samples. E. coli O157:H7 survived longer in rhizosphere soil than the non‐rhizosphere soil. The concentration of E. coli O157:H7/pGFP in rhizosphere soils was ≥ 10⁴ CFU/g in both soils at day 12 based on both plate count and real time PCR, with the clay soil significantly (P = 0.05) higher than the sandy soil. This data showed that E. coli O157H:7 can persist in the environment for more than 50 d, and this may pose some risk for both animal and human infection and provides a very significant pathway for pathogen recontamination in the environment.     

High-performance liquid chromatography determination of residue levels on chicken carcasses treated with cetylpyridinium chloride

Cetylpyridinium chloride (CPC) has been found to be effective in reducing contamination of chicken carcasses from a variety of microorganisms, including Escherichia coli O157:H7, Salmonella typhimurium, Campylobacter jejuni, Aeromonas hydrophila, Listeria monocytogenes, and Staphylococcus aureus. A procedure has been developed to determine residue levels on chicken carcasses after CPC treatment. For the analysis, chicken carcasses were extracted with 95% ethanol. The CPC concentration in the extract was measured by high-performance liquid chromatography (HPLC) with ultraviolet detection using dodecylpyridinium chloride (DPC) as an internal standard. The method was validated in the concentration range of 3–200 μg/ml CPC in ethanolic extract. This assay is rapid, precise, and accurate.     

Use of zero-valent iron biosand filters to reduce Escherichia coli O157:H12 in irrigation water applied to spinach plants in a field setting

Aims:  Zero‐valent iron (ZVI) filters may provide an efficient method to mitigate the contamination of produce crops through irrigation water. Methods:  A field‐scale system was utilized to evaluate the effectiveness of a biosand filter (S), a biosand filter with ZVI incorporated (ZVI) and a control (C, no treatment) in decontaminating irrigation water. An inoculum of c. 8·5 log CFU 100 ml^?1 of Escherichia coli O157:H12 was introduced to all three column treatments in 20‐l doses. Filtered waters were subsequently overhead irrigated to ‘Tyee’ spinach plants. Water, spinach plant and soil samples were obtained on days 0, 1, 4, 6, 8, 10, 13 and 15 and analysed for E. coli O157:H12 populations. Results:  ZVI filters inactivated c. 6 log CFU 100 ml^?1E. coli O157:H12 during filtration on day 0, significantly (P < 0·05) more than S filter (0·49 CFU 100 ml^?1) when compared to control on day 0 (8·3 log CFU 100 ml^?1). On day 0, spinach plants irrigated with ZVI‐filtered water had significantly lower E. coli O157 counts (0·13 log CFU g^?1) than spinach irrigated with either S‐filtered (4·37 log CFU g^?1) or control (5·23 log CFU g^?1) water. Soils irrigated with ZVI‐filtered water contained E. coli O157:H12 populations below the detection limit (2 log CFU g^?1), while those irrigated with S‐filtered water (3·56 log CFU g^?1) were significantly lower than those irrigated with control (4·64 log CFU g^?1). Conclusions:  ZVI biosand filters were more effective in reducing E. coli O157:H12 populations in irrigation water than sand filters. Significance and Impact of the Study:  Zero‐valent ion treatment may be a cost‐effective mitigation step to help small farmers reduce risk of foodborne E. coli infections associated with contamination of leafy greens.     

Effects of vegetable type, package atmosphere and storage temperature on growth and survival of Escherichia coli O157:H7 and Listeria monocytogenes

The survival and growth of Escherichia coli O157:H7 (ATCC 43888 and NCTC 12900) and Listeria monocytogenes (ATCC 19114 and NCTC 11994) during storage (4 and 8°C) on ready-to-use (RTU) packaged vegetables (lettuce, swedes (rutabaga), dry coleslaw mix, soybean sprouts) were studied. The vegetables were sealed within oriented polypropylene packaging film, and modified atmospheres developed in packs during storage due to produce respiration. Survival and growth patterns were dependent on vegetable type, package atmosphere, storage temperature and bacterial strain. Populations of L. monocytogenes and E. coli O157:H7 increased (P<0.05, by 1.5 to 2.5 log cycles, depending on strain) during a 12-day storage period on shredded lettuce (8°C). L. monocytogenes populations also increased (by ∼1 log cycle) on packaged swedes, did not change significantly (P>0.05) in packages of soybean sprouts and decreased by ∼1.5 log cycles (P<0.05) on coleslaw mix (8°C). E. coli O157:H7 populations on packaged coleslaw and soybean sprouts increased (by 1.5 to 2.5 log cycles) up to day 5, but declined during subsequent storage (8°C). On packaged swedes (8°C), populations of E. coli O157:H7 strain ATCC 43888 increased (by ∼1 log cycle) during storage, whereas populations of strain 12900 increased between days 2 and 5, and declined during subsequent storage. Reducing the storage temperature from 8 to 4°C reduced the growth of L. monocytogenes and E. coli O157:H7 on packaged RTU vegetables. However, viable populations remained at the end of the storage period at 4°C. Journal of Industrial Microbiology & Biotechnology (2001) 27, 111–116. Received 25 May 2000/ Accepted in revised form 21 September 2000     

Novel strategies of essential oils,chitosan, and nano- chitosan for inhibition of multi-drug resistant: E. coli O157:H7 and Listeria monocytogenes

Despite the wide range of available antibiotics, food borne bacteria demonstrate a huge spectrum of resistance. The current study aims to use natural components such as essential oils (EOs), chitosan, and nano-chitosan that have very influential antibacterial properties with novel technologies like chitosan solution/film loaded with EOs against multi-drug resistant bacteria. Two strains of Escherichia coli O157:H7 and three strains of Listeria monocytogenes were used to estimate antibiotics resistance. Ten EOs and their mixture, chitosan, nano-chitosan, chitosan plus EO solutions, and biodegradable chitosan film enriched with EOs were tested as antibacterial agents against pathogenic bacterial strains. Results showed that E. coli O157:H7 51,659 and L. monocytogenes 19,116 relatively exhibited considerable resistance to more than one single antibiotic. Turmeric, cumin, pepper black, and marjoram did not show any inhibition zone against L. monocytogenes; Whereas, clove, thyme, cinnamon, and garlic EOs exhibited high antibacterial activity against L. monocytogenes with minimum inhibitory concentration (MIC) of 250–400 μl 100^?1 ml and against E. coli O157:H7 with an MIC of 350–500 μl 100^?1 ml, respectively. Among combinations, clove, and thyme EOs showed the highest antibacterial activity against E. coli O157:H7 with MIC of 170 μl 100^?1 ml, and the combination of cinnamon and clove EOs showed the strongest antibacterial activity against L. monocytogenes with an MIC of 120 μl 100^?1 ml. Both chitosan and nano-chitosan showed a promising potential as an antibacterial agent against pathogenic bacteria as their MICs were relatively lower against L. monocytogenes than for E. coli O157:H7. Chitosan combined with each of cinnamon, clove, and thyme oil have a more effective antibacterial activity against L. monocytogenes and E. coli O157:H7 than the mixture of oils alone. Furthermore, the use of either chitosan solution or biodegradable chitosan film loaded with a combination of clove and thyme EOs had the strongest antibacterial activity against L. monocytogenes and E. coli O157:H7. However, chitosan film without EOs did not exhibit an inhibition zone against the tested bacterial strains.     

Untreated and enzyme‐modified bovine whey products reduce association of Salmonella Typhimurium,Escherichia coli O157:H7 and Cronobacter malonaticus (formerly Enterobacter sakazakii) to CaCo‐2 cells

Aims: Adhesion of a micro‐organism to a cell surface is often considered to be the first step in pathogenesis. Inhibiting this process may have therapeutic effects in vivo. This study investigates the inhibitory effects of various bovine whey products on the association of Salm. Typhimurium, E. coli O157:H7 and C. malonaticus (formerly Enterobacter sakazakii) to the human CaCo‐2 cell line. Invasion of CaCo‐2 cells by Salm. Typhimurium and C. malonaticus was also examined. Methods and Results: Infection assays were performed by incubating pathogenic acteria with CaCo‐2 cells in the presence of untreated (UT) or enzyme‐modified (EM) whey products. Associated micro‐organisms were directly quantified by plate counts. Invasion of CaCo‐2 cells by Salm. Typhimurium and C. malonaticus in the presence/absence of test materials was also quantified using gentamicin protection assays. At a concentration of 40 mg ml^?1, some UT whey products reduced association and invasion, but this effect was enhanced following hydrolysis with porcine pancreatic lipase. Conclusions: Both UT and EM sweet whey protein concentrates (WPCs) were found to be particularly effective inhibitors of association and invasion. All EM whey products significantly (P < 0·05) inhibited invasion of C. malonaticus into epithelial cells, causing a 2‐log reduction in the quantity of these micro‐organisms internalized. Significance and Impact of the Study: The present study suggests that whey products can inhibit association to and invasion of CaCo‐2 cells by selected micro‐organisms and may be useful in the treatment and/or prevention of foodborne infections.     

Fundamental Characteristics of Deep-UV Light-Emitting Diodes and Their Application To Control Foodborne Pathogens

Low-pressure mercury UV (LP-UV) lamps have long been used for bacterial inactivation, but due to certain disadvantages, such as the possibility of mercury leakage, deep-UV-C light-emitting diodes (DUV-LEDs) for disinfection have recently been of great interest as an alternative. Therefore, in this study, we examined the basic spectral properties of DUV-LEDs and the effects of UV-C irradiation for inactivating foodborne pathogens, including Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes, on solid media, as well as in water. As the temperature increased, DUV-LED light intensity decreased slightly, whereas LP-UV lamps showed increasing intensity until they reached a peak at around 30°C. As the irradiation dosage and temperature increased, E. coli O157:H7 and S. Typhimurium experienced 5- to 6-log-unit reductions. L. monocytogenes was reduced by over 5 log units at a dose of 1.67 mJ/cm². At 90% relative humidity (RH), only E. coli O157:H7 experienced inactivation significantly greater than at 30 and 60% RH. In a water treatment study involving a continuous system, 6.38-, 5.81-, and 3.47-log-unit reductions were achieved in E. coli O157:H7, S. Typhimurium, and L. monocytogenes, respectively, at 0.5 liter per minute (LPM) and 200 mW output power. The results of this study suggest that the use of DUV-LEDs may compensate for the drawbacks of using LP-UV lamps to inactivate foodborne pathogens.     

Cattle,weather and water: mapping Escherichia coli O157:H7 infections in humans in England and Scotland

Entero‐haemorrhagic Escherichia coli O157:H7 is a zoonotic pathogen, responsible for a relatively small number of food poisoning and illness outbreaks each year, when compared with other food‐borne bacteria capable of causing infections in the population. Nevertheless, E. coli O157:H7 is a bacterial pathogen associated with severe human illnesses including bloody diarrhoea and haemolytic uremic syndrome occurring in both outbreak and sporadic settings. In England and Wales approximately 1% of all laboratory‐confirmed cases of food poisoning are the result of E. coli O157:H7; however, in Scotland this figure increases to 3%. When the size of the population is taken into account and the rate of E. coli O157:H7 confirmed cases per 100 000 population is examined, the rate of E. coli 0157:H7 infections in Scotland is much greater than England and Wales. The routes of transmission have changed over time, with new routes of transmission such as farm visits emerging. The prevalence of E. coli O157:H7 has a seasonal dependency, with greater faecal shedding of the organism in the warmer months; this is directly mirrored in the increased reporting of E. coli O157:H7 infection among hospitalized patients. This review attempts to suggest why this phenomenon occurs, paying particular attention to weather, animal movement and private water supplies.     

Comparison of four enrichment broths for the detection of non-O157 Shiga-toxin-producing Escherichia coli O91, O103, O111, O119, O121, O145 and O165 from pure culture and food samples

Aims: We compared the efficiency of universal pre‐enrichment broth (UPB), modified Escherichia coli broth containing novobiocin (mEC + n), modified Tryptic Soy Broth (mTSB) and mTSB with novobiocin (mTSB + n) for the enrichment of non‐O157 Shiga‐toxin‐producing E. coli (STEC). Methods and Results: Freeze‐injured and control non‐O157 STEC (O91, O103, O111, O119, O121, O145 and O165) strains were used to artificially contaminate beef and radish sprout samples, which were then cultivated in each of the four enrichment media. After incubation, STEC strains were detected by loop‐mediated isothermal amplification (LAMP) and plating assays. Enrichment in mEC + n was least effective for facilitating the detection of uninjured STEC strains in radish sprouts, while mTSB + n was least effective for enriching freeze‐injured non‐O157 STEC strains from beef samples for detection by LAMP assay. UPB and mTSB were superior to mEC + n and mTSB + n for the enrichment of non‐O157 STEC from food samples. Conclusions: The enrichment of non‐O157 STEC was negatively affected by the addition of novobiocin to enrichment broths. Significance and Impact of the study: Novobiocin should not be added to media used for the enrichment of non‐O157 STEC in food when cell injury is anticipated.     

Viability of zoonotic pathogens Escherichia coli and Salmonella in swine manure slurries with and without a urease inhibitor and thymol

Aims: To determine the effects of urine, a urease inhibitor and/or an odour‐reducing antimicrobial compound, on zoonotic pathogens in swine manure slurries. Methods and Results: Swine faeces were collected and blended with different amounts of urine. Marker strains of Salmonella enterica subsp. enterica serovar Typhimurium and Escherichia coli O157:H7 were inoculated into the manure slurries with or without the urease inhibitor, N‐(n‐butyl) thiophosphoric triamide, or the antimicrobial compound thymol. In slurries containing approximately 1 : 1 or 2 : 1 of urine and faeces, the decreases in colony forming units (CFU) of Salm. Typhimurium and E. coli were similar and few counts were observed after 14 days. When the urine content of the slurry was increased to 5 : 1, both strains died off rapidly. When NBPT was added to the slurries, pathogen CFU was not affected in the 1 : 1 slurry. The 2 : 1 and 5 : 1 slurries had higher urea content and NBPT increased CFU of both pathogens. Thymol addition rapidly killed the pathogens and few CFU of Salmonella or E. coli were observed after day 1. Conclusions: These experiments demonstrate that urea hydrolysis in swine manure affects pathogens. Inhibition of urea hydrolysis may promote pathogen viability. Significance and Impact of the Study: Manure amendments that prevent urea hydrolysis may promote pathogen persistence. Additional treatments with antimicrobials may be required to kill pathogens.     

Examination of indigenous microbiota and survival of Escherichia coli 0157 and Salmonella in a paper milling environment

Aims: A public beach was frequently cited for health advisories because of high Escherichia coli levels, the source suspected to be a paper mill located upstream. This investigation sought to confirm whether or not the paper mill was the pollution source, and to characterize the risk to recreational bathers imposed by the source. Methods and Results: Quantification of E. coli in river water collected at incremental distances showed that paper mill effluent caused elevated E. coli levels in beach samples. Samples collected throughout the mill were variably positive for heterotrophic bacteria, total coliforms and E. coli, but negative for pathogenic E. coli O157 and Salmonella. Escherichia coli O157 or Salmonella spiked into mill samples (4·2 log₁₀ or 5·6 log₁₀ CFU per 100 ml, respectively) fell below detection levels within 14–24 h in raw (unaltered) samples, while in heat‐sterilized replicates, the counts remained at initial levels or increased over 36 h. Conclusions: Pathogenic E. coli O157 and Salmonella were not isolated from paper mill samples. The absence of native bacteria allowed the survival of pathogens, while their presence accelerated pathogen decline. Significance and Impact of the Study: The co‐existence of paper mill and swimming beach may be reasonable for now in spite of the limitations of an E. coli‐based assay for beach water.     

电解水的抑菌活性及对食品加工表面材料的消毒效果

为了考查应用电解水消除细菌污染的可行性,对氧化电解水的杀菌效果及对食品加工表面材料的消毒效果进行了研究。结果表明,含0.1%NaCl的自来水经7min的电解后所获得的氧化电解水,能在2min内将菌液浓度分别为4.20×106CFU/mL,2.18×106CFU/mL,1.44×106CFU/mL,2.10×106CFU/mL,1.94×106CFU/mL的埃希氏大肠杆菌(Escherichia coliO157:H7)、沙门氏菌(Salmonella enteritidis)、单核细胞增生李斯特菌(Listeria monocytogenes)、摩化摩根菌(Morganella morganii)、副溶血性弧菌(Vibrio parahaemolyticus)几乎全部杀死。另外,对食品加工表面接触材料中的地板砖、不锈钢板、瓷砖进行染菌消毒试验结果表明,含0.1%NaCl的电解水同样能将上述浓度的菌液感染到食品表面接触材料后在5min之内几乎全部将其杀死,是一种理想的食品表面材料消毒剂。